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code/filesys/filesys.h

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+// filesys.h 
+//	Data structures to represent the Nachos file system.
+//
+//	A file system is a set of files stored on disk, organized
+//	into directories.  Operations on the file system have to
+//	do with "naming" -- creating, opening, and deleting files,
+//	given a textual file name.  Operations on an individual
+//	"open" file (read, write, close) are to be found in the OpenFile
+//	class (openfile.h).
+//
+//	We define two separate implementations of the file system. 
+//	The "STUB" version just re-defines the Nachos file system 
+//	operations as operations on the native UNIX file system on the machine
+//	running the Nachos simulation.  This is provided in case the
+//	multiprogramming and virtual memory assignments (which make use
+//	of the file system) are done before the file system assignment.
+//
+//	The other version is a "real" file system, built on top of 
+//	a disk simulator.  The disk is simulated using the native UNIX 
+//	file system (in a file named "DISK"). 
+//
+//	In the "real" implementation, there are two key data structures used 
+//	in the file system.  There is a single "root" directory, listing
+//	all of the files in the file system; unlike UNIX, the baseline
+//	system does not provide a hierarchical directory structure.  
+//	In addition, there is a bitmap for allocating
+//	disk sectors.  Both the root directory and the bitmap are themselves
+//	stored as files in the Nachos file system -- this causes an interesting
+//	bootstrap problem when the simulated disk is initialized. 
+//
+// Copyright (c) 1992-1993 The Regents of the University of California.
+// All rights reserved.  See copyright.h for copyright notice and limitation 
+// of liability and disclaimer of warranty provisions.
+
+#ifndef FS_H
+#define FS_H
+
+#include "copyright.h"
+#include "openfile.h"
+
+#ifdef FILESYS_STUB 		// Temporarily implement file system calls as 
+				// calls to UNIX, until the real file system
+				// implementation is available
+class FileSystem:public dontcopythis {
+  public:
+    FileSystem(bool format) { (void) format; }
+
+    bool Create(const char *name, int initialSize) { 
+	int fileDescriptor = OpenForWrite(name);
+	(void) initialSize;
+
+	if (fileDescriptor == -1) return FALSE;
+	Close(fileDescriptor); 
+	return TRUE; 
+	}
+
+    OpenFile* Open(const char *name) {
+	  int fileDescriptor = OpenForReadWrite(name, FALSE);
+
+	  if (fileDescriptor == -1) return NULL;
+	  return new OpenFile(fileDescriptor);
+      }
+
+    bool Remove(const char *name) { return Unlink(name) == 0; }
+
+};
+
+#else // FILESYS
+class FileSystem:public dontcopythis {
+  public:
+    FileSystem(bool format);		// Initialize the file system.
+					// Must be called *after* "synchDisk" 
+					// has been initialized.
+    					// If "format", there is nothing on
+					// the disk, so initialize the directory
+    					// and the bitmap of free blocks.
+
+    bool Create(const char *name, int initialSize);  	
+					// Create a file (UNIX creat)
+
+    OpenFile* Open(const char *name); 	// Open a file (UNIX open)
+
+    bool Remove(const char *name);  	// Delete a file (UNIX unlink)
+
+    void List();			// List all the files in the file system
+
+    void Print();			// List all the files and their contents
+
+  private:
+   OpenFile* freeMapFile;		// Bit map of free disk blocks,
+					// represented as a file
+   OpenFile* directoryFile;		// "Root" directory -- list of 
+					// file names, represented as a file
+};
+
+#endif // FILESYS
+
+#endif // FS_H